Au-coated quartz fabric by plasma treatment as a flexible SERS substrate for rapid detection of harmful substances

Food safety remains a global concern and there is always demanded to advance methods to ensure that toxic substances and contamination do not pose safety concerns. This study discusses the development of a rapid, low-cost, portable, in situ method for the detection of harmful substances on the surface of fruits and vegetables to ensure safety for human consumption. Gold nanoparticles (Au NPs) are deposited onto quartz fabric by using a magnetron sputtering system. The argon flow rate and sputtering time are both controlled to produce Au NPs of different sizes on the quartz fabric with different gap distances. Scanning electron microscope images, X-ray diffraction spectra, and Raman intensity are used to evaluate the produced substrates. With an average grain size of about 32.35 nm, the Au particles with a thickness of 70 nm deposited onto the quartz fabric (i.e., Qt-70) provide the best surface-enhanced Raman scattering (SERS) performance of 65,639 counts towards a 10-3 M methylene blue (MB) solution. The results show that the Qt-70 SERS substrate is highly sensitive, reproducible, and stable, and demonstrates good reusability. Images of "hotspots" that form between two Au nanoparticles based on electric field distribution are simulated by using the finite-difference time-domain (FDTD) method to explain for the signal enhancement. In addition, Qt-70 can be used for the direct collection of pesticides, such as Rhodamine B (RhB), Rhodamine 6G (R6G), and Malachite green (MG), from food surfaces. This novel flexible SERS (FSERS) substrate has good potential for the rapid detection of harmful substances on food.